韩国最高产量研究和水稻高产技术综述


Chae Yun Cho, Yun Jin Oh
韩国农业发展部 Rural Development Administration Suweon, 441-707, Korea


　　原文摘要 ABSTRACT

　　水稻是韩国农民的主要粮食作物和重要收入来源，种稻收入占平均农业收入的一半和农民平均收入的28%。水稻产量已达到很高水平，但水稻生产中仍有许多卡脖子问题，包括有限的土地资源，农场规模小，农场劳力短缺，不正常气候条件，持续增长的人口和对优质大米的需求。需要不断开发更好的水稻品种和更稳定的栽培措施以克服上述难题。水稻育种战略要培育优质品种，将产量由每公顷4.5吨提高到5.l吨；所需劳力由现在的每公顷536人时，减少为低于55人时。

　　Rice is the staple food crop and an important income source for Korean farmers. The income from rice farming occupies about a half of the average agricultural income per farm household and 28% of the average farmer's income. Rice yields have already reached high levels but there are many bottlenecks in rice production. They are limited land resources, small farm size, shortage of farm labor, unusual weather conditions, ever-increasing population, and the demand for good quality rice. Continuous development of better rice varieties and more stabilized cultural practices is required to overcome these difficulties. Rice breeding strategies are to develop high quality varieties to increase the yield from 4.5 t/ha to more than 5.1 t/ha. The labor requirement will be decreased from the present level of 536 man-hours to less than 55 hours per hectare.

　　试验证明根量较大、分布较深与高产紧密相关。株型矮，叶色深绿，叶片窄而直立似乎有益于获得高产。老根吸收60%以上水稻所需的水分、氮、磷和钾，而新根只吸收不到40%。获得高产必须采用最适植株密度，视土壤条件、品种分蘖力、肥力水平、每蔸苗数和播种季节而定。已证明气孔较大的水稻品种是理想的高产农学性状。单位面积小穗数是决定最终产量最重要的产量构成因素。籼-粳稻杂交品种的叶面积指数为7~9时水稻产量最高而粳稻品种最佳叶面积指数为5。粳稻品种的最优施氮量为150公斤/公顷，而籼-粳稻杂交品种为180公斤/公顷。为降低单位面积水稻生产成本，开发并向农民传授了7~8天株龄苗插秧技术。这种技术可使育苗成本下降54%。过去稻农要等苗龄35天时才移栽。高产稻田土壤硬度和容重比对照田块的低。也需要施用有机肥、硅肥和客土等综合土壤改良技术来维持土壤生产力。

　　It was revealed that larger amount of rice roots and their deeper distribution in soils are closely related to a high yield. The short statured plant type with dark green, narrow and erect leaves seemed desirable for obtaining a maximum yield. The old root absorbed more than 60% of the required water, nitrogen, phosphorus and potassium of rice plants, while the new roots did less than 40%. An optimum planting density must be employed to get a high yield, depending upon soil condition, varietal tillering ability, fertilizer level, number of plants per hill, and planting season. A wider stomatal aperture of rice variety proved to be a desirable agronomic character for high yielding. The number of panicles per unit area was the most important yield components in determining final yield. Rice yield reached the maximum at a leaf area index of seven to nine in indica-japonica cross variety, and at a leaf area index of about five in japonica variety, respectively. The optimum nitrogen level was about 150 kg/ha for japonica varieties and 180 kg/ha for indica-japonica cross varieties. In order to cut down rice production cost per unit area, transplanting techniques of 7- to 8-day old seedlings are being developed and disseminated to the farmers. These techniques can decrease 54% of the nursing cost of rice seedlings. In the past years, rice farmers grew the seedlings for more than 35 days before transplanting. The hardness and density of high yielding soils were lower than those of the control plot soils. The integrated soil improvement such as application of organic fertilizers, silica fertilizer, and exotic soils, is needed to maintain soil productivity.

　　1.引言 INTRODUCTION

　　水稻占全国人均粮食消费量的81%以上，是农民主要的收入来源，占49%左右。1960年代全国平均精米产量仅为3吨/公顷。当时栽培的品种大多为粳稻。这些品种多感染稻瘟病和水稻条纹叶枯病毒病。每年因感染不可避免地减产10~15%。粳型稻高杆易倒伏。所以，8~9月间大风和台风严重损害水稻，水稻生产基础不良，因涝、旱、冷和其它灾害而减产严重。

　　Rice occupies more than 81 % of the national average food grain consumption per head and also the principal source of farmer's income, contributing about 49%. The national average milled rice yield was only 35/ha during the 1960's. Most of the varieties under cultivation at that time, were japonica varieties. These varieties were susceptible to blast and stripe virus diseases. An annual yield reduction of 10 to 15% was unavoidable due to these destructive diseases. The japonica varieties were tall and susceptible to lodging. Therefore, they were badly damaged by strong winds and typhoons prevailing in August and September. The production foundations for rice cropping were relatively poor and yield losses from floods, droughts, cold and other disasters, were serious.

　　人们强烈感到，在这种条件下大幅提高水稻产量要开发新的高产品种和栽培技术。水稻育种家的目标是培育综合粳型和籼型稻的理想性状于一体的品种。1965年用早熟耐低温粳稻品种 Yukara与适应性广泛的台湾品种Taichung Native l杂交出第一代，该杂交种又与高产、直立型、矮秆、抗稻瘟病，由国际水稻研究所培育的IR8再次杂交。1970年最终培育出三交种Tongil。Tongil品种的主要农学性状与粳稻型极为不同。在品种改良过程中，用缩短培育周期的技术培育新稻种。1977年引进了花粉培养技术，缩短培育时间和扩大水稻基因变异。这些技术使在7年中培育出优良品种成为可能。已培育出并向农户推广了许多优良水稻品种。1977年创造了全国稻米平均产量4.94吨/公顷的记录，使水稻生产自给自足，这是韩国人民梦寐以求的愿望。如今，人们更偏爱优质大米而不是高产稻米。因此，人们已将育种目标从高产转向口感良好的水稻品种。

　　It was strongly felt that the only way to dramatically increase rice production under these circumstances was the development of new high yielding varieties and cultural technologies. Rice breeders aimed at an integration of desirable characters of both japonica and indica rice types into a single variety. In 1965 the first cross was made between an early-maturing, cold-tolerant Japanese variety, Yukara with a widely adaptable Taiwanese variety, Taichung Native 1. The hybrid plant was again crossed with a high-yielding, erect, short-statured and blast-resistant variety, IR8 which was developed at the International Rice Research Institute. At last, a triplecross variety, “Tongil” was developed in 1970. “Tongil” variety was very different in major agronomic characters from japonica varieties. During the course of this varietal improvement, the techniques for shortening breeding cycle were adopted in developing new rice varieties. The anther culture techniques were also introduced in 1977 in order to shorten the breeding period and to expand genetic variability of rice. These techniques made possible to develop better varieties within seven years of time. Many superior rice varieties have been developed and disseminated to the farmers. The highest national average rice yield, 4.94 t/ha in milled rice, was recorded in 1977, and it resulted in self-sufficiency of rice production which had been a long-cherished desire of Korean people. Nowadays the people prefer high quality rice to high yielding. Accordingly, we have shifted our breeding objectives from increasing productivity into improving palatability of rice varieties.

　　另一方面，为减少单位面积生产成本，急需节省劳力的栽培措施。直到1989年，大多采用35天龄苗插秧，遇到农忙季节人手短缺的问题。自1990年起，大量插栽7~8天龄的秧苗。由于该项技术的实施，插秧所需劳力大为减少，育秧劳力也减至最少。

　　On the other hand, labor-saving cultural practices of rice farming, are urgently needed to minimize the production cost per unit area. By 1989, 35 day old seedlings were mostly transplanted and faced with a shortage of farmhand during the busy transplanting season. Only seven to eight day old seedlings have been extensively transplanted since 1990. Because of this technique, labor requirement for rice transplanting is greatly reduced and the cost of nursing seedling is substantially minimized.

　　2.水稻植株的形态学特点 MORPHOLOGICAL CHARACTERISTICS OF RICE PLANT

　　数量庞大、分布深层的根系一般有益于水稻植株吸收水分，维持气孔开张，在光强度高的情况下光合速率更高。图1示出三个水稻品种齐穗三周后的根系垂直分布。籼-粳杂交品种Suweon 258和Milyang 23比粳型品种 Kanto 116在更深土层产生更多根系。这种深扎根的习性似乎不仅由水稻品种遗传能力控制，而且在于环境条件。

　　The larger amount and deeper distribution of roots were generally favorable for water absorption of rice plant which supports wider stomatal opening and higher photosynthetic rate at a high light intensity. Fig.1 shows vertical distribution of roots three weeks after the full heading stage in three rice varieties. The indica-japonica cross varieties, Suweon 258 and Milyang 23 produced more roots in deep soil layers than the japonica variety, Kanto 116. The habit of rooting in deep soils seemed to be controlled not only by genetic ability of rice variety but also by environmental conditions.

　　Fig.1 Vertical distribution of roots 3 weeks after the full heading stage

(图：图1 齐穗期3周后根系垂直分布图(Terashima 和 Washio,1983))

　　水稻根系生长与水稻全株生长关系密切，见图2。

　　The growth of rice roots was closely related to growth of the whole plant, as shown in Fig.2

　　Fig.2 Relationship between total dry weight and root dry weight of four rice varieties (IRRI, 1978)

(图：图2 四种水稻品种全株干重与根系干重的关系(IRRI,1978))

　　因此，在水稻抽穗前应得到最大根重以获得高产。若其它条件不变。从给定土体中吸收水分、养分速率与总有效根长成正比（Gardrer，1964，1960）。总根长又与水稻植株的养分吸收有关。Okajima（1962）报告了老根吸收60%以上水分、氮、磷和钾，而新根吸收不到40%，见表1。

　　Therefore, it is necessary to get a maximum root weight of rice plant before heading stage to obtain a higher yield. The rate of water and nutrient absorption from a given soil volume was proportional to the effective total root length if other conditions were held constant (Gardner, 1960, 1964). The total root length was also related to absorption of nutrients by rice plant. Okajima（1962）reported that old roots took up more than 60% of water, nitrogen, phosphorus and potassium, while new roots absorbed only less than 40%, as shown in Table 1.

　　Table 1. Absorption of water and nutrients by old and new roots

(表：表1 老根和新根对水分和养分的吸收(Okajima,1962) )

　 Roots 根 Amount absorbed a 吸收量
Dry wt. 干重(g) No. 条数 Max.root length最大根长(cm) H2O(ml) N(mg) P(mg) K(mg)
Old老根 1.75 157 33 155 14 4.5 9.8
64% 62% 63% 63%
New新根 1.32 175 25 86 8.5 2.5 5.7
36% 38% 37% 37%
Total总计 　 　 　 241 22.5 7 15.5

　　每蔸插三株秧苗时，根系深扎的比率高于每蔸五株和七株的。两个品种之间没有深扎根比率的种间差异（图3）。

　　The deeper distribution ratio of roots was higher when three seedlings per hill were transplanted, as compared with those of five and seven seedlings per hill. There was no varietal difference in ratio of roots which rooted into deep soil layers between two rice varieties.

　　Fig.3 Root distribution as affected by number of transplanted seedlings per hill

(图：图3 每蔸秧数对根系分布的影响)

　　深根水稻植株从深层土壤中吸收更多养分、并保护植株在生殖生长阶段不倒伏。

　　Deep rooting of rice plant made easy to absorb more nutrients from deep soil layers, and protected the plant from lodging at reproductive stage.

　　干旱条件下，各水稻品种的根冠比在穗期介于0.05~0.3之间，平均为0.1。土壤由表面开始干燥，但底土潮湿，因此，水稻能吸到有效水。所以在检验水稻品种抗旱性上，深根比浅根更重要。浅根、高分蘖品种在植物根茎周围根密度很大，但根系同时向垂直和水平方向生长。另一方面，深根、低分蘖品种根系分布间距适当、侧向生长、深层土壤中的根系比浅根、高分蘖品种活力更强。表2表明，高产试验小区比对照小区表土中和底土中根系都更多。

　　The root-shoot ratio of rice varieties ranges from 0.05 to 0.3 at heading, averaging about 0.1 under drought condition. Soils start to dry from the surface but subsoils may remain wet so that rice roots can absorb available water. Consequently, deep roots are more important than shallow roots in examining drought resistance of rice variety. A shallow-rooted, high-tillering variety has a very high root density around the plant base but the roots grow vertically as well as laterally. On the other hand, a deep-rooted, low-tillering variety has a well-spaced, lateral root distribution and its roots grow more actively in deep soils than those of a shallow-rooted, high-tillering variety. The plot of high yielding trial showed more roots not only in top soils but also in subsoils, as compared with those of the control plot as shown in Table 2.

　　Table 2. Root distribution as affected by high yielding trial with different soil depths

(表：表2 不同土层深度受到高产试验影响和根系分布 )

Soil depth土层深度 (cm)厘米 (D) Root amount (g/m2)根量(克/米2)
Control对照 High yield trial高产试验
0 - 15 (A) 359 472
15 - 30 (B) 67 142
30 - 45 (C) 430 620
Index 指数 100 144
Ratio of deep portiona深层根系所占比例(%) 16 24

注释：注：a=(B+C)/D×100
　　籼-粳杂交品种一般气孔大，中午光强度高时气孔也不关闭。因此，这一特性在高产能力上起重要作用。一般地说，水稻叶片直立与水稻品种高产有关，这一习性可使光照传到低位叶片，使植株光合作用更活跃。厚叶片比薄叶片具有更多叶绿体。高产品种的理想叶片特征一般是直立、厚实、短窄型。粳型稻种植冠叶片低垂，比叶片直立的籼-粳稻的生物量低。低垂植冠的叶片对低位叶片起遮光作用，使后者在黑暗条件下的呼吸作用加强。结果最终生物量会下降。改良水稻的光合能力比老品种的提高40%。

　　Indica-japonica cross varieties generally had a wider stomatal aperture and no stomatal depression at noon even at high light intensity. Consequently, this character may play an important role in yielding ability. In general, it is known that erectness of rice leaf is associated with high yielding of rice variety. This habit allows light to transmit to the lower rice leaves and results in active photosynthesis of rice plant. Thicker rice leaves had more chloroplast than thin leaves. Ideal leaf characteristics for high yielding seemed to be erect, thick, short, and narrow types. Varieties like japonica type which have a canopy of drooping leaves, produce lower biomass than those like indica-japonica cross type with erect leaves. Drooping canopy of leaves causes shading to lower leaves and may enhance respiration of leaves under dark condition. Eventually, final biomass activities may decline. The photosynthetic ability of the improved rice varieties has been increased by 40% as compared with the old varieties.

　　3.高产的生理学原理 PHYSIOLOGICAL ASPECTS FOR HIGH YIELDING

　　水田水稻光合活性主要决定于入射阳光辐射、叶片取向、单位叶面积光合速率、叶面积指数、温度、氮效应和生育期，尤其是在温带地区。图4所示稻生产潜力估计值表明，温带地区比热带地区单位土地生产力更高。

　　Rice photosynthetic activity in the field is primarily determined by incident solar radiation, leaf orientation, photosynthetic rate per unit leaf area, leaf area index, temperature, nitrogen response, and growth duration, particularly in the temperate zone. The estimated potential rice yield shown in Fig.4 indicated that the temperate zone is more productive than the tropics in terms of per unit land yield.

　　Fig.4 Relationship between potential yield and incident radiation during the grain filling period of rice (IRRI, 1977).

(图：图4 水稻籽粒灌浆期潜在产量和入射辐射的关系(IRRI,1997))

　　韩国的试验站中最高产量记录是9.7吨/公顷精米。国际水稻研究所的最高产量是11吨/公顷精米，日光辐射估计值为550卡/厘米2/天。与叶角度和叶片尺寸等叶片构造有关的水稻植冠强烈影响光截留量。传统水稻品种叶片低垂，随着叶面积增大、会限制阳光穿透到低位叶片。Oh等（1979）指出，小而直立的水稻叶片有利于阳光穿透到低位叶片。一般认为，直立株型消光系数小（图5）。

　　The recorded maximum yield was 9.7 t/ha in milled rice in the experiment station of Korea. Tile International Rice Research Institute got a maximum yield of II t/ha in milled rice, with an estimated solar radiation of 550 cal/cm' per day. Rice canopy related to leaf architecture including leaf angle and size, strongly affects light interception. The traditional rice varieties with drooping leaf arrangement, limit light penetration into the lower leaves of rice plant as leaf area index increases. Oh et al. (1979) suggested that small and erect rice leaves are favorable for light transmission to the lower leaves. It is generally accepted that small extinction coefficient is related with erectness of plant type, having a smaller value when the leaves are erect (Fig.5).

　　Fig.5 Relationship between leaf area index and light transmission ratio (Kwon and Park, 1972)

(图：图5 叶面积指数和透光比的关系(Kwon和Park,1972))

　　叶面积指数常用于作物生长分析。叶面积指数小于4时，叶片倾斜度不很重要（Duncar，1971）。但是叶面积指数高时它对作物增产至关重要。图6示出籼-粳杂交品种Tongil和Milyang 23的叶面积指数7~9时水稻产量最高，而粳稻品种Jinheung在叶面积指数5时产量最高。两个籼-粳杂交品种在高产试验中比粳稻品种叶面积指数高得多。当叶面积指数提高后，低位叶片被遮更多，加剧了呼吸。

　　The leaf area index has been extensively used for crop growth analysis. Leaf inclination was not so important when the index was less than four (Duncan, 1971). However, high leaf area index was essential for increasing crop yield. Fig.6 shows that rice yield reached a maximum level at a leaf area index of seven to nine in the indica-japonica cross varieties like Tongil and Milyang 23, while the japonica variety, Jinheung did a maximum level at an index of five. The two indica-japonica rice varieties had much higher index than the japonica variety in the high yielding trial. The lower leaves were more shaded and their respiration seemed to be accelerated as the index increases.

　　Fig.6 Relationship between rice yield and leaf area index

(图：图6 水稻产量和叶面积指数的关系)

　　极低、极高范围内的温度影响小穗生成、成熟和最终籽粒产量。基本上说，高温促进叶片萌出速率并加速分蘖出芽。然而，随着温度下降每株发育更多小穗。换言之，水稻生长最适温度在营养生长阶段高，而生殖生长阶段低。韩国等温带国家从营养生长到生殖生长阶段温度的改变似乎有利于水稻获得高产。因此认为，韩国的温度条件刺激水稻营养生长期的光合作用和生殖生长期光合产物的转运。

　　Temperature within extremely low and high levels, affected spikelet formation, ripening, and final grain yield. Basically, high temperature promoted the rate of leaf emergence and accelerated budding of tillers. However, more spikelets per plant were developed as the temperature decreases. In other words, the optimum temperature for rice growth was high at vegetative stage and low at reproductive stage. The change of temperature from vegetative stage to ripening stage in temperate country like Korea seemed very favorable in obtaining a high yield. Therefore, it is considered that our temperature condition for rice activates photosynthetic activities at vegetative stage, and translocation of photosynthate at reproductive stage.

　　氮是水稻高产栽培中最重要的养分。氮提高了营养生长期和生殖生长前期的产量能力，加速灌浆期同化物的生成。生育早期吸收的氮大多数用于产生水稻茎等营养器官，后期吸收的氮用于产生籽粒。所以，茎杆和籽粒生长的氮效率视其不同生育期适宜供应量而定。过去15年中随着籼-粳杂交品种的发展，氮肥用量持续增长。氮水平提高时高产品种产量增加，但稻米品质比不上一些优质品种。韩国水稻消费者偏爱优质米而不是劣质米。因此，稻农只种具有与籼-粳杂交品种农学特性相同的优质品种。

　　Nitrogen is the most important nutrient for high yielding cultivation of rice plant. It enlarges yield capacity during the vegetative and early reproductive stages, and accelerates production of assimilates at the grain filling stage. Nitrogen absorbed at early growth stage is mostly used to produce vegetative organs like rice straw, and that absorbed at later growth stage is used to produce grains. Therefore, nitrogen efficiency for growth of both straw and grains is depended upon its optimum supply at the different growth stage. The amount of nitrogen fertilizer had been steadily increased along with the development of the indica-japonica cross varieties during the last 15 years. The high yielding varieties gave higher yields at increased nitrogen levels but the rice quality was not comparable to that of some high quality varieties. Korean rice consumers prefer better quality rice to low quality rice. Therefore, rice farmers grow only high quality varieties which have similar desirable agronomic characters to those of the indica-japonica cross varieties.

　　Yoshida和Parao（1976）报导了生殖生长阶段CO2增加和遮荫大大影响水稻植株养分汇的大小，也报导过生殖生长阶段日光辐射和最终产量呈显著正相关。这些事实表明，光合作用对水稻植株养分汇大小的影响巨大。这也表明植株组织中含氮量高促进更多小穗分化，而及时从叶片向小穗供应光合产物减少了生殖生长期小穗的退化。因此找到了营养生长期平均温度和籽粒产量之间的高度负相关。营养汇的形成视氮和光合产物的分配平衡而定。

　　Yoshida and Parao (1976) reported that CO2 enrichment and shading during the reproductive stage, influenced very much the sink size of rice plant. It was also reported that there was a high positive correlation between solar radiation during the reproductive stage and final grain yield. These facts indicate a great effect of photosynthetic activity on the size of sink of rice plant. They also imply that high nitrogen content in the plant tissues brings about promoted differentiation of more spikelets, and that prompt supply of photosynthates from leaves to spikelets minimized degeneration of spikelets during the reproductive stage. Thus, a high negative correlation between mean temperature during vegetative period and grain yield was found. Sink formation is depended upon balance of partitioning of nitrogen and photosynthates.

　　Murayama（1967）年指出小穗生长效率（由抽穗前吸收的氮单位形成的小穗数计算），在较冷气候下比较暖地区为高。Yoshida等（1972）用国际水稻研究所品种证实了这点。国际水稻研究所小日月品种在旱季的小穗形成效率与小日月粳稻品种相同，原因是热带旱季条件下，营养生长阶段温度不那么高。可将小日月品种小穗形成能力高归因于小穗分化初期叶鞘中的氮含量高。

　　Murayama (1967) pointed out that efficiency of spikelet formation (evaluated by spikelet number per nitrogen unit absorbed before heading) is high in cooler climates than in warmer regions. Yoshida et al. (1972) confirmed this result using IRRI varieties. The efficiency of spikelet formation of IRRI short-duration varieties in dry season was similar to that of short-duration japonica variety. The reason is that the temperature of vegetative stage in dry season in the tropics was not so high. High ability of spikelet formation of short-duration varieties could be attributable to high nitrogen content in leaf sheath at panicle initiation stage.

　　水稻植株的小穗形成也很受生殖生长阶段植株组织中氮含量的影响（Kumura，1956）。作物苗的早期生长很易由提高种植密度或增施基肥获得。籽粒产量也可由良好调节形成营养汇和氮及光合产物分配过程得以增加。改良小日月品种的基因对高产有很大潜力。

　　Spikelet formation of rice plant is also greatly affected by nitrogen content in plant tissue during reproductive stage (Kumura, 1956). Initial growth of crop stands can be easily obtained by an increase of planting density or by application of increased level of basal fertilizers. Grain yield can be also increased by a fine tuning of the processes related to partitioning of nitrogen and photosynthates for sink formation. Genetic improvement of short-duration varieties has a great potential for high yielding.

　　籽粒成熟涉及两个主要过程，营养汇的确定即成熟百分比的确定，和籽粒成长充填已确定的汇容。粒重与成熟百分比高度相关。这可能表明抽穗前的小穗发育限制籽粒大小。籽粒生长涉及两个生理过程：利用当前光合作用生成的光合产物，和重新动员和转运开花前积累的物质。从叶和叶鞘中积极转运碳水化合物和氮化合物实际上加速这些营养器官衰老。当环境条件不利，成熟期碳水化合物供应量低时，叶片衰老很快。叶和叶鞘衰老缓慢和汇容较大对获得高产是理想的。小日月品种有益于引进多熟种植制度、最大限度利用土地资源。小日月品种也有缺点，其籽实品质差，不抗倒伏。营养生长阶段温度高，促进初期营养生长，但因减少生殖生长阶段小穗形成而减少汇容。成熟期高温，降低作物生长速率和缩短成熟期，使得成熟不良。

　　Seed ripening involves two major processes, sink determination or ripening percentage determination, and grain growth to fill determined sink capacity. Grain weight was highly correlated with ripening percentage. This may indicate that spikelet development before heading limits grain size. Two physiological processes are involved in grain growth: utilization of photosynthates through current photosynthesis, and remobilization and translocation of the accumulated substance before anthesis. Active translocation of carbohydrate and nitrogenous compounds from leaf and leaf sheath will naturally accelerates senescence of the vegetative organs like leaf and leaf sheath. Leaf senescence may be faster when supply of photosynthates during ripening is low due to unfavorable environmental conditions. Slow senescence of leaf and leaf sheath, and larger sink size are desirable to get a maximum yield. Short-duration varieties are beneficial for introduction of a multiple cropping system to maximize utilization of land resources. Short-duration variety has also some disadvantages. They are poor in grain quality and lodging resistance. High temperature at vegetative stage promotes initial vegetative growth but reduces sink size because of reduced spikelet formation at reproductive stage. High temperature at ripening stage causes poor ripening due to reduction of crop growth rate as well as ripening period.

　　4.高产栽培措施 CULTURAL PRACTICES FOR HIGH YIELDING

　　大多数籼-粳杂交品种在韩国分蘖力相对较高。Kim和Vergnara（1991）最近指出，低分蘖株型和大穗可高产。但图7显示每蔸7株生成更多小穗。这可能说明每蔸7株小区在营养生长早期阶段就已发育成较多蘖头。直接播种栽培时低分蘖品种表现更好，这时种植密度更大。

　　Most of indica-japonica varieties showed a relative high tillering abilities in Korea. Kim and Vergara (1991) recently suggested that a low-tillering plant type with large panicle gave a high yield. However, seven seedlings per hill produced more panicles as shown in Fig.7. This may imply that more tillers were already developed at earlier vegetative growth stage in the plots of seven seedlings per hill. Low-tillering variety may perform better in direct-seeded cultivation in which planting density is relatively closer.

　　Fig.7 Effective high yielding ability as affected by number of transplanted seedlings per hill

(图：图7 每蔸秧数对高产能力的影响)

　　高产能力似乎与水稻品种汇容有关。汇容定义为单位面积土地上的穗数、每穗小穗数和平均小穗重。穗数的确定通常先于小穗数的确定。必须保证生长前期足够的蘖数才能得到更多穗。穗数和每穗小穗数由后继阶段可利用光合产物和养分决定。Wada和Matsushima（1962）报导了水稻生殖生长阶段氮的吸收和可利用碳水化合物大大影响穗数的确定。表3表明单位面积土地上的穗数是最重要的产量组成因素。试验II中穗数最多，产量为 8.29吨/公顷糙米。

　　The high yielding ability seems to be related with sink capacity of rice variety. The sink capacity is defined as the product of panicles per unit land area, spikelets per panicle, and average spikelet weight. Determination of panicle number generally precedes determination of spikelet number. Enough tillers must be secured at early growth stage to get more panicles. Number of panicles and spikelets per panicle is finally determined by available photosynthates and nutrients during succeeding stages. Wada and Matsushima (1962) reported that the determination of panicle number is greatly affected by both nitrogen uptake and availability of carbohydrate at reproductive stage of rice plant. Table 3 shows that panicle number per unit land area was the most important yield component. Trial II with highest panicle number produced 8.29 t/ha in brown rice.

　　Table 3. Effect of panicle number among yield components to determine high yielding ability

(表：表3 产量构成因素中穗数对高产能力的影响 )

High yielding trials 高产试验 Panicle number 穗数 Spikelet number per panicle 每穗小穗数 Ripened成熟穗 1000 brown rice grain weight 粗稻粒千粒重 Brown rice yield 粗稻产量
　 (No/m2)株/米2 　 （%） (g)克 (t/ha) 吨/公顷
Trial Ⅰ 试验1 441 92 66 22 7.22
Trial Ⅱ 试验2 532 81 71 19.3 8.29
Trialb Ⅲ 试验3 469 104 69 19.8 8.06

　　可根据茎杆和叶鞘的弯曲运动和折断力物理测定倒伏（Chang，1964）。增施氮肥对高产十分必要，但它造成下部茎节，尤其是最低两个茎节的伸长，使水稻植株容易倒伏。结果，现代韩国水稻品种具有禾茎短硬的特点。提高钾水平来维持水稻禾茎细胞的高膨压，与抗倒伏有关。包裹最低两个茎节的叶鞘也应坚硬。一些栽培技术要求在成熟期尽量保持叶鞘的活性。

　　Lodging can be physically examined in terms of the bending movement and the breaking strength of the culm and leaf sheath (Chang, 1964). Increased nitrogen application which is essential for high yielding, causes elongation of the lower internodes, particularly the lowest two internodes, makes rice plants more susceptible to lodging. Accordingly, modern Korean rice varieties have shorter and stiffer culm characters. Increase of potassium level is associated with increase of lodging resistance through maintenance of high turgor pressure in cells of rice culm. The leaf sheath enclosing the lowest two internodes should be stiff too. Some cultural practices are required to keep these leaf sheaths active during ripening stage.

　　低垂长叶的传统品种株型高，在高氮水平下成熟期易倒伏，往往减低籽粒产量。矮秆直立株型的高产品种在高氮水平下增产，它们可高度防止倒伏和主要病虫侵害。一般推荐对粳稻品种施用150公斤N/公顷，而对籼-粳杂交稻施180公斤N/公顷。氮钾肥常在插秧、分蘖和幼穗分化始期分期施用。

　　The traditional varieties with long, drooping leaves and tall stature decreased grain yield at higher nitrogen levels and were badly damaged by lodging at ripening stage. The high-yielding varieties with short and erect plant type increased grain yield at higher nitrogen levels. They were highly resistant to lodging and some major destructive pests. It is generally recommended to apply about 150 kg N/ha for japonica varieties and about 180 kg N/ha for indica-japonica cross varieties. Split application of nitrogen and potash fertilizers at transplanting, tillering and panicle initiation is commonly practiced.

　　插秧两周后的分蘖期施氮可促进有效蘖生长，而且在幼穗分化始期施肥可加快光合产物向营养汇的转运。在该试验的土壤条件下，维持对水稻植株供钾充足可使产量最高。我们的高产试验中发现硅肥明显改善对倒伏等环境压力的抗性。而且发现，化肥深施到根区中使产量大为增加。

　　Application of nitrogen fertilizer at tillering stage, about two weeks after transplanting, promoted the growth of effective tillers. Also, potassium top-dressing at panicle initiation stage, accelerated translocation of photosynthates to sinks. A sustained supply of potassium to rice plant is necessary to produce a maximum yield under our soil conditions. In our high yielding trials we found out that silicon fertilizer was very useful for improvement of resistance to some environmental stresses like lodging. In addition, it was revealed that deep placement of fertilizers into root zones give a substantial yield increase.

　　有机肥似乎对改善土壤肥力和土壤性状很有效。当施用了30吨/公顷堆肥后水稻产量最高。施用堆肥可能对生长后期土壤缓慢释放氮有所贡献。因深翻排水良好的土壤使表层土壤中有机质迅速分解，所以必须施用有机质。表4示出韩国高产水稻试验中的施肥水平和土壤改良剂。

　　Organic fertilizers seemed very effective on improving soil fertility as well as soil properties. The highest rice yield was obtained when 30 t/ha compost was applied. Application of compost may contribute to a slow release of nitrogen at later growth stage of rice plant. Since deep plowing of well-drained soils quickly decomposes organic matters in top soils, additional organic matters are needed. Table 4 shows input levels of fertilizers and soil ameliorators for high yield trials of rice in Korea.

　　Table 4. Fertilizers and soil amendments applied for hiah yielding trial

(表：表4 高产试验中施肥和土壤改良措施 )

Fert. and soil amendments 施肥和土壤改良 Control 对照 High yielding高产试验
N (kg/ha)公斤/公顷 180 260
P2O5 (kg/ha)公斤/公顷 110 220
K2O (kg/ha)公斤/公顷 130 340
Compost (kg/ha) 堆肥（公斤/公顷） 15,000 30,000
Si. -fertilizer (kg/ha) 硅肥（公斤/公顷） - 1,000
Soil addition (t/ha) 土壤添加剂（吨/公顷） 　 50
Zeolite (t/ha) 沸石（吨/公顷） - 10
Plowing layer (cm) 耕层深度（厘米） 12 25

　　建议稻农在拔节和成熟期间断灌溉稻田，这一措施据信能对根区提供足量氧，移走一些有毒物质，最终导致水稻植株健康茁壮。高产农田水稻土的特点是土壤质地或为粗壤或为细壤，排水良好。由表5所示，高产土壤的硬度、容重和孔隙度与对照土壤截然不同。因此，必须改良水稻土性质以获得最高产量。

　　An intermittent irrigation at tillering and ripening stages is recommended to rice farmers. This practice is believed to supply enough oxygen to root zones, to remove some toxic substances, and finally to make rice plant healthier. The paddy soils in high-yielding fields are characterized by the soil texture of either coarse loam or fine loam with good drainage. As shown in Table 5, hardiness, bulk density and porosity of the high yielding soils, are quite different from those of the control. Therefore. it is necessary to improve properties of paddy soils to get maximum yields.

　　Table 5. Some physical characteristics of the soils used for high yielding trials

(表：表5 高产试验供试土壤的物理性质 )

Physical Characteristics物理性质 Control对照 High yielding trial高产试验
Surface soil表土 Subsoil底土 Surface soil表土 Subsoil底土
Hardiness (mm) 硬度（毫米） 18 22 16 19
Bulk density (g/cm3) 容重（克/厘米3） 1.36 1.66 1.27 1.59
porosity (%) 孔隙度（%） 49 37 52 40

　　韩国水稻农业面临一些困难，诸如农场规模小、农业劳力紧缺、不寻常的气象灾害和病虫危害。我们水稻研究的目的是培育高产，优质，抗病虫抗逆境条件的品种；创造低投入技术，包括节省劳力的栽培技术；综合防治病虫害和发展机械化。我们也致力于开发水稻生产以外的其它农场收入来源。这样才能加强水稻生产的国际竞争力，并使农民收入达最高水平。

　　Korean rice farming is faced with difficulties such as small farm size, shortage of farmhand, unusual weather damages, and destructive pests. Our rice research, is aimed at development of high-yielding, good quality, and pest- and stress-resistant varieties, and at generation of low-input techniques including labor-saving cultural practices, integrated pest control and mechanization. We also focus on development of other farm income resources than rice farming. In this way we can improve the international competitiveness of rice farming and maximize the farmer's income.

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